The present invention relates to a piston diaphragm pump of the type comprising a housing made of several portions clamped to each other by bolts.
Piston diaphragm pumps for pumping a liquid medium, for example hydraulic oil, of the type under consideration include a housing, in which a feeding chamber, connected to a medium inlet and a medium outlet via respective valves, is provided, in which a diaphragm is sealingly clamped between at least two housing portions which are releasably connected to each other. The pump further includes a piston working chamber which in operation is filled with a hydraulic medium and in which a piston is reciprocally displaced for the generation of stroke deflections of the diaphragm, changing volumes of the feeding chamber. The housing portions are connected to each other by clamping bolts provided with threaded portions screwed in respective threads provided in the housing portions.
With conventional piston diaphragm pumps of the type under discussion the housing portions which enclose the diaphragm therebetween are clamped to each other by the clamping bolts wherein both the clamping force of the diaphragm and also a force intercepting the inner pressure exerted on a medium being pumped are provided by the torque applied to the nuts of the bolts externally of the pump housing. Thereby an overall minimal clamping force of each clamping bolt loads the diaphragm surface of the diaphragm clamped between the housing portions and this force is therefore limited by a highest permissible surface pressure. With such plastics as PTFE utilized for diaphragms operation pressures above 325 bar are not realizable in conventional pumps because the increase of the size of the clamping surface can not substantially reduce the surface pressure on the diaphragm.
For high pressures normally steel diaphragms are utilized, which can provide due to increased sensitivity only a short service life of the pumps. Dimensions of such pumps are substantially greater and the manufacture of the double diaphragm is much more expensive. The utilization of a position control with steel diaphragms is not possible.